BCL9 and precursor B-cell acute lymphoblastic leukemia: For instance: (i) lens development is unaffected in mice with targeted deletion of the BCL9-HD2 domain19; (ii) BCL9 acts independently of β-catenin transcription during dental enamel formation3; (iii) BCL9 binds to proteins that transmit signals from estrogen and androgen receptors20; and (iv) the BCL9/MEF2D fusion protein found in patients with poor-prognosis B-ALL lacks the BCL9-HD2 domain21,22.